filter/sample
&
hold (fsh-1a)

Sound
Clips

Bass

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Guitar

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This
is
the Maestro Filter/Sample & Hold project from JD
Sleep's
site. The second foot switch (the one on the left)
is for switching
between Filter and Sample & Hold. The on/off status
indicator is a
bicolor LED, green for Filter, red for Sample & Hold.
In addition
to including all of Tonda's mods, I added a couple of
others. Here are my layout and PCB
transfer files.

I used a MAX1044 chip, as described by R.G.
at GEOFX, to make a bipolar (+/- 9V) supply
that can be powered from a 9VDC wall wart or a single 9V
battery. It's
a nice, easy way to deal with 9V bipolar power
requirements. But, in
this pedal, the battery option is more of a novelty than a
practical
option. This circuit draws something like ~38mA. So, I'm
not even sure
if a battery would even get you through one gig. No big
deal, tho. I'm
planning to use the wall wart, exclusively.

The other mod that I added was a wet/dry balance control.
For bass
players, this a nice mod to do on any pedal. And, it's
especially easy
to do on this pedal. If you check out the schematic on JD Sleep's
site, you'll notice that it includes a non-true
bypass option (the
switch at the output jack). Just replace that switch with
a linear
taper pot (wire the center lug to the output, one wiper to
the C2/R4
junction, the other wiper to the C4/R14 junction). I used
a 500Kb pot,
but other values would probably work, too.

As for that 'noise' transistor in the S&H section, I
think I've
settled on an NTE123AP (same as 2N222A). But, I also got
reasonably
nice randomness with NTE161, 2N5308, 2N3392, and MPSA13.
It took me
some time to get those on-board trimmers set just right,
too. R27 seems
especially touchy. I'm still thinking about replacing it
with a
multi-turn. The 12K resistor on the copper side of the
board is only
there because I didn't have a 10K trimmer handy, so I used
a 47K
instead.